This application is based on Japanese Patent Application Nos. 2000-277226 filed Sep. 12, 2000 and 2001-081642 filed Mar. 21, 2001, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a cylinder pump suitable for sucking two different types of liquid and an ink jet printing system using the cylinder pump, specifically to an improvement for down-sizing of the cylinder pump. The present invention further relates to a photograph assembly having an ink jet printing system provided with the down-sized cylinder pump.
2. Description of the Prior Art
As an ink jet printing system, there has heretofore been a so-called serial scan type equipped replaceably with a recording head as recording means and an ink tank as an ink vessel on a carriage movable in a main scanning direction. This printing method successively prints an image on a printing medium by repeating main scanning of a carriage equipped with the recording head and an ink tank and sub-scanning of the printing medium.
When considering realization of an ultra-compact printer suitable for use in PDA (Personal Digital Assistants) or cameras, it is necessary to reduce the size of the carriage itself. Therefore, the ink volume of the ink tank equipped thereon must be extremely small.
When the ink tank volume on the carriage is extremely small as described above, there is a possibility of generating a problem in that replacement frequency of the ink tank becomes high or the ink tank must be replaced in the course of printing operation.
Then, in order to solve such a problem, there is proposed an ink supply method in which ink is supplied from a separately provided main tank to a sub-tank on the carriage at an appropriate timing every time the carriage is positioned at a predetermined stand-by position, hereinafter for convenience called a pit-in ink supply method.
In this pit-in ink supply method, for example, every time a sheet of printing medium is printed, the carriage is positioned at a predetermined stand-by position, the sub-tank on the carriage and the main tank are connected at an appropriate timing, so that with this connection state, ink is supplied from the main tank to the sub-tank. By this operation, the above-described problem with the ink volume of the sub-tank on the carriage is solved.
In the above-described pit-in ink supply method, an ink absorber such as a sponge is provided inside the sub-tank, ink supply is performed by a negative pressure introduced from an air suction opening to the inside, so that ink is introduced from the main tank into the sub-tank through the ink intake.
Further, in the ink jet printing method, when air influxes into the nozzle of the recording head, or when ink increases in viscosity by drying or the like, the nozzle becomes ink ejection impossible, and ink droplets cannot be ejected from such a nozzle. Therefore, a capping member for covering a face of the recording head and suction means for sucking ink from the nozzle of the recording head through the capping member are provided so that ink which does not contribute to image printing is sucked and removed from the tip of the nozzle at an appropriate time.
As described above, in ink jet printing using the pit-in ink supply method, a suction pump is required for sucking air for ink supply and for sucking ink from the recording head.
As the suction pump, there has heretofore been a tube pump for generating a negative pressure in the cap utilizing the restoration force of a tube squeezed by a roller or a piston pump utilizing a movement of a piston, or the like.
In the case of the tube pump, since a rotary mechanism for rotating the roller for squeezing the tube is required, the mechanism itself becomes large in size. Therefore, it is not suited as a suction pump for the above-described ultra-compact printer.
In the case of the piston pump, since it is a reciprocal type, it is suited as a suction pump for ultra-compact printer. However, also in the case of the piston pump, there are problems of requiring a suction pump which is large in construction such that,
(1) separate pumps are used for ink suction and air suction,
(2) when a common pump is used for ink suction and air suction, a suction switching construction is necessary for switching the ink suction passage and the air suction passage for connecting to the input port of the pump.
As described above, for realizing an ultra-compact ink jet printer suitable for PDA or camera, construction of the suction pump part suitable for ultra-compact structure has been in demand.
Under such circumstances, it is therefore an object of the present invention to provide a cylinder pump which can be constructed small in structure and is suitable for sucking two different types of liquid and an ink jet printing system using the cylinder pump.
In an aspect of the present invention, a cylinder pump unit comprises a cylinder pump and a piston driving means. The cylinder pump includes a reciprocally movable piston and a cylinder main body having a first cylinder chamber partitioned at one side of the piston and introduced with a first fluid and a second cylinder chamber partitioned at the other side of the piston and introduced with a second fluid.
The piston driving means reciprocally moves the piston of the cylinder pump.
In another aspect of the present invention, the first fluid is air, the second fluid is ink and a piston shaft of the piston is extended to outside the cylinder main body through the second cylinder chamber and connected to the piston drive means.
In another aspect of the present invention, the second cylinder chamber has an input port for sucking ink and an output port for discharging ink. A cylinder pump unit further comprises port switching means for performing switching of opening and closing of the input port and output port in association with movement of the piston. Therefore, when the second cylinder chamber is pressure reduced by movement of the piston, the output port is closed and the input port is opened, and when the second cylinder chamber is pressurized by movement of the piston, the input port is closed and the output port is opened. The port switching means is incorporated preferably in the second cylinder chamber.
In another aspect of the present invention, the second cylinder chamber may have an input port for sucking ink, the piston shaft has a hollow cylindrical form, and the hollow part may be an output port for discharging ink. The cylinder pump unit further comprises port switching means for performing switching of opening and closing of the input port and output port in association with movement of the piston. Therefore, when the second cylinder chamber is pressure reduced by movement of the piston, the output port is closed and the input port is opened, when the second cylinder chamber is pressurized by movement of the piston, the input port is closed and the output port is opened.
In another aspect of the present invention, the port switching means is a check valve provided in a passage communicating with the input port and a check valve provided between the piston and the piston shaft.
In another aspect of the present invention, the piston driving means comprises a screw rod engaging with the piston shaft in the piston shaft and rod driving means for rotatively driving the screw rod.
In another aspect of the present invention, the piston driving means may comprise a pump driving arm for connecting through the piston shaft, a lead screw engaging with the pump driving arm for reciprocally driving the pump driving arm and screw driving means for rotatively driving the lead screw.
In another aspect of the present invention, the first cylinder chamber may be connected with an air suction part provided with a porous film in an ink tank. The air suction part introduces a negative pressure that supplies ink from intake into the ink tank. The piston shaft is a hollow cylindrical body and provided with a relief valve at a tip of the piston shaft for maintaining suction pressure of the first cylinder chamber at less than a predetermined pressure. A setting relief pressure of the relief valve is preferably set smaller than a pressure capable of maintaining performance of the porous film.
In another aspect of the present invention, cross sectional form of the cylinder pump may be elliptical.
In another aspect of the present invention, an ink jet printing apparatus comprises an ink tank, a cap, a cylinder pump and piston driving means. The ink tank has an air suction part provided with a porous film, the air suction part introduces a negative pressure that supplies ink from an intake into the ink tank. The cap caps an ink ejection opening of a recording head capable of ejecting ink supplied from the ink tank. The cylinder pump includes a reciprocally movable piston, a cylinder main body having a first cylinder chamber partitioned at one side of the piston and connected with the air suction part, and a second cylinder chamber partitioned at the other side of the piston and connected with the cap. The piston driving means reciprocally moves the piston of the cylinder pump. Air in the ink tank is sucked through the air suction part of the ink tank by the first cylinder chamber of the cylinder pump, and ink is sucked from the cap by the second cylinder chamber of the cylinder pump.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.